Dural Venous Sinuses

Describe Briefly the Meninges Covering Brain.

The three layers of meninges that cover brain are:

Duramater

• Is tough, fibrous, outermost layer.
• Epidural space separates duramater from skull bones.
• Subdural space separates it from arachnoid mater.
• Has two layers – outer endosteal and inner meningeal.

Arachnoid mater

• Thin transparent layer connected to piamater by web like trabeculae.
• Is separated from piamater by subarachnoid space which is filled with CSF and contains the main blood vessels supplying brain.
• Forms arachnoid villi that project into dural venous sinuses and help in drainage of CSF.

Pia mater

• Closely applied to the brain and dips into the sulci.

Name and Describe the Folds of Duramater.

There are four folds of duramater, two in median plane (falx cerebri) and two lie horizontally (diaphragma sellae and tentorium cerebelli).

Falx cerebri

• Is sickle shaped of dura mater lying between the two cerebral hemispheres.
• Extends from crisa galli to the tentorium cerebelli.
• Its upper margin is attached to innere surface of vault of skull and it encloses superior sagittal sinus.
• Its free lower margin contains inferior sagittal sinus.

Falx cerebelli

• Small sickle shaped fold between the two cerebellar hemispheres.
• Superiorly it is attached to tentorium cerebelli and posteriorly to internal occipital crest.
• Encloses occipital sinus along its posterior margin.

Tentorium cerebelli

• Is a crescentic fold that separates cerebellum from the occipital lobes of cerebrum.
• Its free anterior concave border bounds tentorial notch and is attached to anterior clinoid process.
• Its attached from apex of one petrous bone to the other. Posterolaterally the attached margin encloses transverse and sigmoid sinuses on either side.
• Superior petrosal sinus is present in attached anterolateral margin.

Diaphragma sellae

• Is a horizontal fold that forms roof of hypophyseal fossa and covers pituitary gland.
• It has a central aperture for the infundibulum (hypophyseal stalk).

What are the characteristic features of Dural venous Sinuses?

• Dural venous sinuses are venous channels  that are present usually the two layers of dura mater.
• They are lined by endothelium.
• They do not have muscle in their walls.
• They have  no valves.
• They drain blood from
  • Brain
  • Meninges
  • Cranial bones
• They also drain CSF.
• They communicate with veins outside the cranial cavity via emissary veins.

Name the Unpaired and Paired Dural Venous Sinuses

Unpaired dural venous sinuses

• Superior sagittal sinus
• Inferior sagittal sinus
• Straight sinus
• Occipital sinus
• Anterior intercavernous sinus
• Posterior intercavernous sinus
• Basilar plexus of veins

Paired dural venous sinuses

• Cavernous sinuses
• Superior petrosal sinuses
• Inferior petrosal sinuses
• Transverse sinuses
• Sigmoid sinuses
• Sphenoparital sinuses
• Petrosquamous sinuses
• Middle meningeal veins

Which Venous Channels Other Than Dural Sinuses Drain Blood From the Cranial Cavity?

Basilar plexus of veins

• Are interconnecting venous channelspresent on the basilar part of occipital bone.
• Are connected to the inferior petrosal sinuses.
• Communicate inferiorly with the intervertebral venous plexuses.

Diploic veins

• Are located in the diploe of the skull bones ( venous spaces between the outer and inner tables of the flat skull bones.
• Are valveless.
• Are connected to the dural venous sinuses via emissary veins.

Emissary veins

• Small veins that connect dural venous sinuses to the extracranial and diploic veins.
• Do not have valves.
• Their function is to equalize the venous pressure within and outside the cranium.

Applied Aspects